What to know about coronavirus booster shots

"The simplest answer is that it’s just another dose of a vaccine you received," Albert Shaw, a Yale Medicine infectious diseases expert, said last week. "The concept is to prolong protective immunity, particularly if there is evidence that protection is waning after a period of time."

Booster shots are common against other diseases, including against tetanus and diphtheria.

According to news reports, an announcement is imminent from the Biden administration recommending that all people get a booster shot against the virus eight months after their second dose. Boosters could be offered as soon as the middle of September.

The virus delta variant, which was first discovered in India, is proving more infectious and dangerous than previous versions of the disease. Some parts of the United States are being overwhelmed with cases, and hospitals are once again nearing capacity. Even with the vaccine, there are so-called breakthrough cases of vaccinated people. The rates of those cases are higher than initially expected.

For now, the recommendation is set to apply for Pfizer-BioNTech and Moderna, each of which comes in a two-dose series. While those who got the Johnson & Johnson shots, which are a single dose, are also expected to need boosters, the government’s recommendation is pending the company’s clinical trials, expected later in August.

The U.S. Food and Drug Administration has authorized a booster for Pfizer-BioNTech and Moderna vaccines for those who are immunosuppressed. For example, on Tuesday, the medical systems of Weill Cornell, NewYork-Presbyterian and Columbia said that this week they are prioritizing people in those categories, including patients on active treatment for tumors and malignancies, recipients of transplants, and those getting chemo, among other conditions.

The rollout would likely be similar to how vaccinations were distributed when the shots first became available in December 2020 — health care workers, nursing home residents, emergency workers, to be followed by older people and then the rest of the population.

It is hard to get a full picture comparing the rates of reinfections versus so-called breakthrough cases, because of the way data is tracked in New York State, and how it is, and isn’t, disclosed. For example, in New York City, for the first 6 1/2 months of 2021, there were 5,217 people who had COVID-19 once and are known to have caught it again — representing 1.1% of total positive tests, Mayor Bill de Blasio's spokesperson Laura Feyer said in an email. Feyer didn't immediately respond to a follow-up request seeking comparable numbers and rates of so-called breakthrough cases. The state health department has not provided statistics comparing breakthrough cases and reinfections.